[Add the following to section 3.2.3 on Offscreen Rendering]

    To create a GLXPbuffer call:

        GLXPbuffer glXCreateGLXPbufferSGIX(Display *dpy,
                                           GLXFBConfig config,
                                           unsigned int width,
                                           unsigned int height,
                                           int *attrib_list);

    This creates a single GLXPbuffer and returns its XID. <width> and <height>
    specify the pixel width and height of the rectangular pbuffer and
    <attrib_list> specifies a list of attributes for the pbuffer. Currently
    only three attributes can be specified in <attrib_list>:
    GLX_PRESERVED_CONTENTS_SGIX, GLX_LARGEST_PBUFFER_SGIX and
    GLX_DIGITAL_MEDIA_PBUFFER_SGIX.

    [Add following the section on the GLX_PRESERVED_CONTENTS_SGIX attrib]

    The resulting pbuffer, when made current, will contain color buffers 
    and ancillary buffers as specified by <config>. It is possible to create 
    a pbuffer with back buffers and to swap the front and back buffers by 
    calling glXSwapBuffers. Note that some pbuffers use framebuffer resources 
    so applications should consider deallocating them when they are not in use.

    If the GLX_DIGITAL_MEDIA_PBUFFER_SGIX attribute is set to True in
    <attrib_list>, then one or more of the pbuffer's color or ancillary 
    buffers may be shared with those of a currently associated DMbuffer.  
    Buffers described by the pbuffer's GLXFBConfig which are not defined
    by the DMbuffer, are GLX resources that remain associated with the
    DM pbuffer until it is destroyed.
    An implementation may fail glXCreateGLXPbufferSGIX and generate a
    BadMatch error when the sepcified <config> does not describe a  
    drawable that is compatible with any supported DMbuffers.

    The GLXPbuffer is associated with a DMbuffer by calling:

        Bool glXAssociateDMPbufferSGIX(Display *dpy,
                                       GLXPbufferSGIX pbuffer,
                                       DMparams *params,
                                       DMbuffer dmbuffer);

    The parameter <display> specifies a connection to an X server, and must 
    match the display used to create the GLXPbuffer <pbuffer>.  The 
    DMparams <params> arg specifies the digital media characteristics
    of the <dmbuffer> that will be associated with the DM pbuffer.  
    If glXAssociateDMbufferSGIX succeeds, any previously associated DMbuffer
    is released and a value of True is returned.  Subsequent GL commands 
    effect <dmbuffer> as they would any standard pbuffer.  If a newly 
    released DMbuffer has no remaining clients, its buffers will also be freed. 
    A BadMatch error is generated when the specified DMparams or DMbuffer
    are not compatible with the <pbuffer>, and a value of False is returned.

    Before the DM pbuffer can be made current to a GLXContext, it must 
    be associated with a compatible DMbuffer.  glXMakeCurrentReadSGI will 
    return False and generate a GLXBadDrawable error when a DM pbuffer 
    drawable has no associated DMbuffer.

    A GLXPbuffer is destroyed by calling:

        void glXDestroyGLXPbufferSGIX(Display *dpy,
                                      GLXPbuffer pbuf);

    The GLXPbuffer will be destroyed once it is no longer current to any
    client. When a GLXPbuffer is destroyed, any memory resources that
    attached to it, are freed, and its XID is made available for reuse.
    Associated DMbuffers are released, and if they no lonnger have a 
    client, are also freed. 

Errors

    XXX - not complete yet

New State

    None.

New Implementation Dependent State

    None.